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Monday, August 22, 2016

NASA’s
managers have begun the process for a competition to select a new planetary
mission to launch in the mid-2020s that will address one of the most important
questions in planetary science.The
winning proposal will be the fourth mission in the agency’s New Frontiers
program that sent the New Horizons craft to Pluto, the Juno orbiter to Jupiter,
and will launch the OSIRIS-REx mission next month to return a sample from a
primitive asteroid.

Previously selected New Frontiers missions. Credit: NASA

NASA’s
planetary missions fall into three categories of ambition and cost.At the high end at around $2-2.5 billion are
the Flagship missions that use highly capable spacecraft for exploration that
addresses a wide range of questions at the target world.These missions include the Curiosity Mars
rover, its 2020 Mars rover sibling in development, and the planned Europa
multi-flyby mission.

At the
low end, at around $600 million, are the Discovery missions that conduct highly
focused missions.Teams are free to
propose missions to study any solar system body except the Sun and Earth (which
are studied through other programs at NASA). Ten of these planetary missions have flown successfully and have included the
MESSENGER spacecraft that orbited Mercury and the DAWN spacecraft that
currently orbits the asteroid Ceres.Next up will be the 2018 InSight geophysical station for Mars to be
followed by one or two missions to study either asteroids and/or Venus that
will be selected by the end of the year.

At a total cost
of somewhere around $1 billion, the New Frontiers missions fit between these
two programs in ambition.The goal for
these missions are to address focused high priority science questions.
The scientific community selects the candidate themes through the
Decadal Survey in which a long list of scientist-proposed ideas are
vetted and prioritized.

The next New
Frontiers mission will be selected from among a list of the six mission themes
that the planetary science community identified as as highest priority to answer key
questions about our solar system:

Comet Surface Sample Return
– Enable in-depth laboratory analysis of the most primitive material left form
the formation of the solar system

Lunar South Pole-Aitken Basin
Sample Return – Enable in-depth laboratory analysis of material from our moon
to understand the how the bombardment of the inner solar system worlds by
comets and asteroids effected their formation

Saturn Atmospheric Probe – Determine
the composition of Saturn’s atmosphere to help us better understand the
formation of the solar system

Trojan Asteroid Tour and
Rendezvous – Explore a reservoir of remnant bodies from the formation of the
solar system to understand how materials from different regions of the early
solar system mixed during planetary formation

Venus
In Situ Explorer –
Understand the formation, evolution, and current state of the atmosphere
and surface of our sister world that evolved into a hell

Ocean Worlds (Titan and/or
Enceladus) – Do these two moons of Saturn have the conditions to support life
and is life present?

The first five of these themes were selected through the Decadal Survey. NASA’s managers added
the Ocean Worlds theme in response to a Congressional directive and further
discoveries by the Cassini mission.For
the next, fifth New Frontiers competition, Jupiter’s moon Io and a lunar geophysical
network theme will be added.

NASA’s
managers currently expect to select a New Frontiers mission from the list of
themes approximately every five years.At that pace, completing this series of investigations, including the
new themes for the next selection, will require around forty years (assuming no
changes to the list from future Decadal Surveys).The pressure on each proposing team to have
their proposal selected now rather than waiting decades must be intense.(If this long time frame seems disheartening,
some of the themes may be addressed by other space agencies.A European team, for example, is proposing a
Saturn atmospheric probe to the European Space Agency.NASA Discovery missions may also partially
address some of the themes.Among the
five proposals competing to be among the next Discovery missions are spacecraft
that would address several of the atmospheric objectives of the Venus theme and
address the Trojan theme through flybys rather than the proposed New Frontiers
orbiter plus flybys approach.)

For some
of the themes, the Decadal Survey listed (and NASA’s managers have adopted)
very specific research goals.Any team
proposing a mission for the Venus in situ explorer, for example, must propose a
probe that would descend through the atmosphere and likely land on the surface.
Here are the objectives from the draft document announcing NASA’s request for
proposals (called an Announcement of Opportunity (AO)):

The Venus In Situ Explorer mission theme is focused on
examining the physics and chemistry of Venus’s atmosphere and crust by
characterizing variables that cannot be measured from orbit, including the
detailed composition of the lower atmosphere, and the elemental and
mineralogical composition of surface materials. The science objectives (listed
without priority) of this mission theme are:

Understand the physics and chemistry of Venus’s
atmosphere through measurement of its composition, especially the abundances of
sulfur, trace gases, light stable isotopes, and noble-gas isotopes;

Constrain the coupling of thermochemical,
photochemical, and dynamical processes in Venus’s atmosphere and between the
surface and atmosphere to understand radiative balance, climate, dynamics, and
chemical cycles;

Understand the physics and chemistry of Venus’s
crust;

Understand the properties of Venus’s atmosphere
down to the surface and improve understanding of Venus’s zonal cloud-level
winds;

Understand the weathering environment of the
crust of Venus in the context of the dynamics of the atmosphere of Venus and
the composition and texture of its surface materials; and

Search for evidence of past hydrological
cycles, oceans, and life and constraints on the evolution of Venus’s
atmosphere.

This is
an ambitious list, and the AO specifically states that proposers can select,
but must thoroughly justify their selection, a subset of these goals.

By
contrast, the goals for the Trojan asteroid tour and rendezvous reflect the
fact that we know very little about these never-visited bodies that share
Jupiter’s orbit.This population of
small worlds represent fragments left over from the formation of the
planets.The diversity of the
composition of these worlds will allow scientists to select from among
competing models for how the solar system formed.The requirements for this theme are short:

The Trojan Tour and Rendezvous mission theme is intended to
examine two or more small bodies sharing the orbit of Jupiter, including one or
more flybys followed by an extended rendezvous with a Trojan object. The science
objective of this mission theme is:

·Visit, observe, and characterize multiple
Trojan asteroids

The briefness of
the requirements for the Trojan theme likely makes life harder for teams
proposing a mission to these worlds.In
judging proposals, NASA’s review teams will score proposals on their scientific
merit (~40% of score), the feasibility of the specific proposed instruments and
measurements (~30%), and overall mission feasibility within the cost cap
(~30%).Scientific merit includes an
explanation of the, “Compelling nature
and scientific priority of the proposed investigation's science goals and
objectives. This factor includes the clarity of the goals and objectives…”Teams proposing for Venus have the benefit of
goals developed and specified by the Venus science community while teams
proposing for the Trojans have to develop and defend their own list of specific
science goals and objectives.

(At the end of
this post, I’ve copied the specific goals for the remaining mission themes from
the AO.)

Missions proposed
for the next New Frontiers program will need to meet many criteria including
these:

Total
cost for the development of the spacecraft, the instruments, and analysis of
the returned data cannot exceed $850 million.NASA will separately pay for the mission’s launch and operation costs
while in flight (likely several tens of millions of dollars per year), which together
probably will bring the total cost of the mission to $1 billion or more.

Proposals
can include instruments paid for by foreign governments, but the costs of these
instruments cannot exceed one-third of the cost of the total instrument
compliment.As one NASA manager put it,
NASA invests a great deal of money to develop instrument technologies by
American scientists, and it wants to see a return on that investment by having
the majority of instruments on the selected mission be American.

Teams
can propose the use of radioisotope heaters and radioisotope electrical power
generators for their missions.These
units would be useful for missions operating far from the sun (for example, at
Saturn).However, a mission using these
units would need to reserve a substantial portion of the core $850 million to
cover the cost of these units.Using
just the heaters would incur a cost of $47-79 million (depending on the number)
and the electrical power generators would cost $133-195 million (again based on the
number of generators used).These costs
could drastically reduce the capabilities of the spacecraft and instruments
compared to missions that don’t require these technologies.

I suspect that
for many readers of this blog, a mission to return to Enceladus or Titan to
continue their exploration with a new generation of spacecraft and instruments
would be a personal favorite.I share
that desire, but also recognize the challenges any proposal to these worlds
would face.First, these worlds were
just added to the list of candidate themes in the past few months.The in-depth analysis of objectives for these
missions is just getting underway by the scientific community.Second, the technical maturity of instruments
to explore their oceans, determine their habitability, and search for life may
be low – NASA has not made major investments in these technologies for these
worlds (but plans to begin to do so).And third, these missions are likely to need radioisotope power
generators and their cost would eat significantly into the mission budget,
potentially making it less competitive.(Solar powered missions are possible at Saturn, but appear to be on the
edge technically.This could make a
proposal that depends on solar power appear technically risky.)Balancing these negatives is a heritage of
three Discovery-class proposals to these worlds that were not selected but
which could form the basis of a New Frontiers-class mission.Still, I personally doubt that a mission to
these moons will be selected this time.(If I am wrong, given a mid-2020’s launch and a flight that could last
10 years, it could be the mid-2030s before the spacecraft arrives at its
target.)

I’ve learned to
not try to predict which Discovery or New Frontiers mission is likely to be
selected from the list of proposals made.The scrutiny given these proposals is intense.Any fault with the details of a proposal can
rule it out.If the review panel decides
that a proposed key engineering manager doesn’t have sufficient experience,
that could kill a proposal.If the
review panel concludes that a technology proposed to be used for the spacecraft
or a key instrument lacks maturity, that could kill a proposal.If the review panel concludes that the
specific set of scientific objectives proposed are not as compelling as for
other proposals, that could kill a proposal.No matter how sexy a proposal might look from the limited information
that we in the general public get to see, faults in the details that we never
see may rule it out.

However, we need
to remember that all the candidate themes for the upcoming selection of the
fourth New Frontiers mission represent questions deemed to be among the highest
priority for exploring the solar system.Whichever mission is finally selected will significantly expand our
understanding of the solar system.

Schedule for the
next New Frontiers competition and launch:

Final AO Release Date -- January 2017 (target)

Deadline for Receipt of
Proposals -- AO Release + 3 months + 4 days

Selection of a subset
(historically, two) of proposals for further study -- November 2017 (AO release
+ 10 months)

Final selection -- July 2019
(target)

Launch --
December 31, 2024 if solar powered or December 31, 2025 if radioisotope power
sources are required

Flight time to
the target world: Days (the moon), months (Venus), years to a decade or more
(comet with Earth return, Saturn, or Trojan asteroids)

The Comet Surface Sample Return mission theme is focused on
acquiring and returning to Earth a macroscopic sample from the surface of a
comet nucleus using a sampling technique that preserves organic material in the
sample. The mission theme would also use additional instrumentation on the
spacecraft to determine the geologic and geomorphologic context of the sampled
region. Because of the increasingly blurred distinction between comets and the
most primitive asteroids, many important objectives of an asteroid sample
return mission could also be accomplished by this mission. The science
objectives (listed without priority) of this mission theme are.

The Lunar South Pole-Aitken Basin Sample Return mission
theme is focused on returning samples from this ancient and deeply excavated
impact basin to Earth for characterization and study. In addition to returning
samples, this mission would also document the geologic context of the landing
site. The science objectives (listed without priority) of this mission theme
are:

• Elucidate the nature of the Moon’s lower crust and/or mantle by
direct measurements of its composition and of sample ages;

• Determine the chronology of basin-forming impacts and constrain
the period of late, heavy bombardment in the inner solar system, and thus,
address fundamental questions of inner solar system impact processes and
chronology;

• Characterize a large lunar impact basin through “ground truth”
validation of global, regional, and local remotely sensed data of the sampled
site;

• Elucidate the sources of thorium and other heat-producing
elements to understand lunar differentiation and thermal evolution; and

• Determine the age and composition of farside basalts to determine
how mantle source regions on the Moon’s farside differ from the basalts from
regions sampled by Apollo and Luna

The Ocean Worlds mission theme is focused on the search for
signs of extant life and/or characterizing the potential habitability of Titan
and/or Enceladus. For Enceladus, the science objectives (listed without
priority) of this mission theme are:

• Assess the habitability of Enceladus’ ocean; and

• Search for signs of biosignatures and/or evidence of extant
life.

For Titan, the science objectives (listed without priority) of the
Ocean Worlds mission theme are:

• Understand the organic and methanogenic cycle on Titan,
especially as it relates to prebiotic chemistry; and

The Saturn Probe mission
theme is intended to deploy one or more probes into Saturn’s atmosphere to
directly determine the structure of the atmosphere as well as noble gas abundances
and isotopic ratios of hydrogen, carbon, nitrogen, and oxygen. The science
objectives (listed without priority) of this mission theme are:

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.